Method and Apparatus for Determining Quality of Radio Maps

ABSTRACT

In accordance with an example embodiment of the present invention, an apparatus comprises a processor configured to determine a first result of estimating a position based at least in part on a first partial radio map, the processor further configured to perform a first comparison of the first result to a reference position, and a memory configured to store a second result based upon the comparison.

TECHNICAL FIELD

The present application relates generally to determining quality ofradio maps.

BACKGROUND

Modern global cellular and non-cellular positioning technologies arebased on generating large global databases containing information oncellular and non-cellular signals. The information may originateentirely or partially from users of these positioning technologies. Thisapproach may also be referred to as “crowd-sourcing”.

Information provided by users may be in the form of “fingerprints”,which contain a location that is estimated based on, for example,received satellite signals of a global navigation satellite system,GNSS, and measurements taken from one or more radio interfaces forsignals of a cellular and/or non-cellular terrestrial system. A locationmay comprise an area surrounding a geographical position, for example.In the case of measurements on cellular signals, the results of themeasurements may contain a global and/or local identification of thecellular network cells observed, their signal strengths and/or pathlosses and/or timing measurements like timing advance, TA, or round-triptime. For measurements on wireless local area network, WLAN, signals, asan example of signals of a non-cellular system, the results of themeasurements may contain at least one of a basic service setidentification, BSSID, like the medium access control, MAC, address ofobserved access points, APs, the service set identifier, SSID, of theaccess points, and the signal strengths of received signals. A receivedsignal strength indication, RSSI, or physical reception level may beexpressed in dBm units with a reference value of 1 mW, for example.

Such data may then be transferred to a server or cloud, where the datamay be collected and where further models may be generated based on thedata for positioning purposes. Such further models can be coverage areaestimates, communication node positions and/or radio channel models,with base stations of cellular communication networks and access pointsof WLANs being exemplary communication nodes. In the end, these refinedmodels, also known as radio maps, RM, may be used for estimating theposition of mobile terminals.

Fingerprints do not necessarily have to comprise a GNSS based position.They may also include cellular and/or WLAN measurements only. In thiscase the fingerprint could be assigned a position for example based on aWLAN based positioning in a server. Such self-positioned fingerprintscan be used to learn cellular network information, in case there arecellular measurements in the fingerprint. Moreover, in a set of WLANmeasurements in a fingerprint there may be, in addition to measurementsfor known WLAN access points, also measurements for unknown accesspoints and the position of the unknown access points can be learnedthrough these self-positioned fingerprints. Finally, more data can belearnt of previously known access points based on self-positionedfingerprints.

It may be noted that even when using a mobile terminal havingGNSS-capabilities, a user may benefit from using cellular/non-cellularpositioning technologies in terms of time-to-first-fix and powerconsumption. Also, not all applications require a GNSS-based position.Furthermore, cellular/non-cellular positioning technologies work indoorsas well, which is generally a challenging environment for GNSS-basedtechnologies.

SUMMARY

Various aspects of examples of the invention are set out in the claims.

According to a first aspect of the present invention, an apparatuscomprises a processor configured to determine a first result ofestimating a position based at least in part on a first partial radiomap, the processor further configured to perform a first comparison ofthe first result to a reference position, and a memory configured tostore a second result based upon the comparison.

According to a second aspect of the present invention, a methodcomprises determining a first result of estimating a position based atleast in part on a first partial radio map, and performing a firstcomparison of the first result to a reference position.

According to a third aspect of the present invention, a method comprisesdetermining a first result of estimating a position based at least inpart on a first partial radio map, performing a first comparison of thefirst result to a reference position, determining a third result ofestimating the position based at least in part on a second partial radiomap, performing a second comparison of the third result to the referenceposition, and determining a quality of the first partial radio maprelative to a quality of the second partial radio map based at least inpart on the first comparison and the second comparison.

According to further aspects of the present invention, computer programsare provided that are configured to cause methods in accordance with thesecond and third aspects to be performed.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of example embodiments of the presentinvention, reference is now made to the following descriptions taken inconnection with the accompanying drawings in which:

FIG. 1 shows an example architecture of a positioning system;

FIG. 2 shows an example system for generating and distributing partialRMs for offline usage in user terminals;

FIG. 3 shows an apparatus embodying a process for determining a qualityof a partial radio map according to an example embodiment of theinvention;

FIG. 4 is a flow diagram showing operations for determining quality ofpartial radio maps in accordance with at least one embodiment of theinvention; and

FIG. 5 demonstrates how quality of two batches of partial radio maps maybe compared, according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

Positioning systems may function in two modes. The first mode is aterminal-assisted mode, in which a terminal performs measurements ofcellular and/or non-cellular air interface signals and provides resultsof the measurements to a positioning server hosting a global cellularand/or non-cellular RM database. The server then provides a positionestimate back to the terminal. This methodology is called onlinepositioning and requires the terminal to have data connectivity wheneverpositioning service is needed.

The second mode is a terminal-based mode, an offline positioningtechnique, in which a terminal has a local copy of a RM, called apartial RM. This partial RM is a subset of the global RM in form of WLANRM offline files, for example. These files may be in the form of adatabase or any other form that is readable by a computer. There may bemultiple such files, since it may be advantageous not to have a singleglobal file, but several smaller ones so that the terminal may onlydownload partial RM for a specific area, for example, a country or acity where a need for positioning is anticipated. This subset can alsobe pre-installed on the terminal. Offline positioning techniques do notrequire the terminal to have data connectivity whenever positioningservice is needed.

Offline positioning may be advantageous from a service perspectivebecause it helps reduce load on positioning servers. Also, since theterminals are capable of positioning themselves without contacting apositioning server, the terminals may remain location aware all thetime. Additionally, time-to-first-fix may be very short, since thedevice does not need to contact the server.

WLAN RM offline files can be very large in size. As an example, in anurban/suburban area covering roughly 10×10 km, there can be more than 10million APs. This results in an average density of one AP every 10 m² or400,000 APs per 2×2 km tile. Transferring location information for eachof these APs from a server to a terminal consumes a lot of serverresources, network bandwidth, storage space in the terminal and it canalso be quite expensive to the consumer in the form of data charges. Inaddition, WLAN AP environments may be highly dynamic and new APs mayappear, existing APs may become obsolete and AP locations may change,for example. Resultantly, radio maps installed on a device may need tobe refreshed, possibly more than once, with their newer versions. Hence,it is preferable to have small WLAN RM offline files.

To reduce size of a radio maps and corresponding WLAN RM offline files,those APs which do not significantly affect any of accuracy,availability and consistency of a radio map may be excluded from theradio map. Availability of a positioning system is defined as the ratioof the number of successful positioning events to the total number ofpositioning requests. Consistency of a positioning system is a measureof a quality of its uncertainty estimate. An estimate of a locationbased upon a radio map may not be a point but rather it may be an area,also known as an uncertainty area, centered at a point such that thetrue location is estimated to be comprised with the uncertainty area. Anuncertainty area of a radio map may be a circle or an ellipse, forexample. Consistency of a positioning system indicates how likely it isthat a true location will be comprised within an uncertainty area.Consistence may be expressed in percentage. For example, a 95% level ofconsistency implies that a true location will fall inside an indicateduncertainty area in 95% of the cases. It can be appreciated thataccuracy, availability and consistency are important metrics affectinguser experience. A further reduction in size of a partial radio map filemay be achieved by compressing identifiers of APs comprised in thepartial radio map, into less number of bits by utilizing a digitalcompression algorithm. But even after excluding APs from a partial radiomap and utilizing compressed AP identifiers, sizes of partial radio mapfiles may still be prohibitively big for frequent downloads by userterminals. Thus, it is desirable to avoid downloading a newer version ofa partial radio map to a user terminal as much as possible, while stillmaintaining an acceptable level of accuracy and availability in offlinepositioning.

Embodiments of the present invention relate to comparing positioningoutput of a partial radio map to a reference location and based upon thecomparison, determining whether a new partial radio map should bedownloaded by a user terminal or not. Another embodiment of theinvention relates to comparing a positioning output of a first partialradio map to a reference location and comparing a positioning output ofa second partial radio map to the same reference location and based uponthe comparisons, determining a relative quality of the two partial RMs.

FIG. 1 shows an example architecture of a positioning system. Thepositioning system of FIG. 1 comprises a GNSS 101, a user terminal 102,a cellular network 103. WLAN systems 104, a positioning server 105, acollection/learning server 106 and a global RM database 107. Positioningserver 105 and collection/learning server 106 may be co-located in asingle site or apparatus, or alternatively they may be distinct in thesense that positioning server 105 is external to collection/learningserver 106 and collection/learning server 106 is external to positioningserver 105. Global RM database may be a standalone node, or it may becomprised in collection/learning server 106 and/or positioning server105. The user terminal 102 may receive its GNSS based position from theGNSS 101. The GNSS could be GPS, GLONASS or any other satellite basednavigation system. The user terminal may also receive radio signals fromthe cellular network 103. The cellular network 103 could be based on anykind of cellular system, for instance a GSM system, a 3rd GenerationPartnership Project, 3GPP, based cellular system like a WCDMA system ora time division synchronous CDMA, TD-SCDMA, system. for examplesupporting high speed packet access, HSPA, a 3GPP2 system like aCDMA2000 system, a long term evolution, LTE, or LTE-Advanced system, orany other type of cellular system, like a WiMAX system. Cellular network103 comprises a plurality of base stations or base transceiver stationsas communication nodes. Furthermore, user terminal 102 may also receivesignals from WLANs 104. WLANs 104 comprise at least one access point asa communication node. WLANs 104 may be based upon the IEEE 802.11standards, for example.

The user terminal 102 comprises a processor 1021, and linked to theprocessor, a memory 1022. Memory 1022 stores computer program code inorder to cause the user terminal 102 to perform desired actions.Processor 1021 is configured to execute computer program code stored inmemory 1022. The user terminal further comprises memory 1024 to storeadditional data such as, for example, partial RMs. The user terminal mayfurther include at least one antenna in communication with at least onetransmitter and at least one receiver to enable communication with theGNSS 101, cellular network 103, WLANs 104, positioning server 105 andcollection/learning server 106. The mobile terminal processor 1021 maybe configured to provide signals to and receive signals from the atleast one transmitter and the at least one receiver, respectively.

Although not shown, the user terminal 102 may also include one or moreother means for sharing and/or obtaining data. For example, theapparatus may comprise a short-range radio frequency, RF, transceiverand/or interrogator so data may be shared with and/or obtained fromelectronic devices in accordance with RF techniques. The user terminalmay comprise other short-range transceivers, such as, for example, aninfrared, IR, transceiver, a Bluetooth™ BT, transceiver operating usingBluetooth™ brand wireless technology developed by the Bluetooth™ SpecialInterest Group, a wireless universal serial bus, USB, transceiver and/orthe like. The Bluetooth™ transceiver may be capable of operatingaccording to low power or ultra-low power Bluetooth™ technology, forexample, Bluetooth low energy, radio standards. In this regard, the userterminal 102 and, in particular, the short-range transceiver may becapable of transmitting data to and/or receiving data from electronicdevices within proximity of the apparatus, such as within 10 meters, forexample. The apparatus may be capable of transmitting and/or receivingdata from electronic devices according to various wireless networkingtechniques, including 6LoWpan, Wi-Fi, Wi-Fi low power, IEEE 802.15techniques, IEEE 802.16 techniques, and/or the like.

The user terminal further comprises a collection client 1023. Collectionclient 1023 may comprise, for example, a software module stored inmemory 1022, or in another memory comprised in user terminal 102. Thecollection client 1023 may be configured to collect informationcomprising at least one of the following to be sent to thecollection/learning server 106:

An estimate of the user terminal's location based on, for example,received satellite signals of the GNSS 101

Measurements taken from signals of the cellular network 103.

Results of scanning of WLAN systems 104.

Results of scanning of other short range radio signals.

The collection/learning server 106 receives this information and basedon it, builds a database of AP locations and coverage areas of cellularbase stations and APs, such as for example WLAN APs. Such a database maybe called a global RM database 107 since the RMs stored in this databasemay not be specific to a country or a city. Rather, they may be globalin nature. In some embodiments, collection/learning server 106 isconfigured to build a database of AP locations that does not compriseinformation on coverage areas of cellular base stations.

Once a reliable global RM database 107 is built, the positioning server105 may serve online positioning requests from user terminals. A userterminal may take measurements of signals from cellular networks and/orperform WLAN scans and send them to the positioning server 105. Thepositioning server may refer to the global RM database and based atleast in part upon the information provided by the user terminal,provide an estimate of the user terminal position.

If a data connection between the positioning server and a user terminalis unavailable or is undesirable, the terminal may rely on thepositioning engine 1025 to serve positioning requests offline. A partialRM or a subset of the global RM in form of RM offline files, such as forexample WLAN offline files, may be stored in the memory 1024 of the userterminal. With a partial RM pertaining to the area in which a userterminal is presently located stored in a memory of the user terminal,the user terminal may scan the WLANs and/or signals from cellularnetworks at its location and provide a list of observed AP identifiersand/or base stations identities to the positioning engine 1025. Afterconsulting a partial RM stored in the user terminal 102 and based uponthe observed AP identifiers and/or the base station identities, thepositioning engine 1025 may estimate a location of the user terminalwithout sending a request to a positioning server. It should be notedthat partial RMs may be based upon access points of short range wirelesssystems other than WLAN systems and a user terminal may scan for signalsfrom at least one of these other short range wireless systems toestimate its position.

FIG. 2 shows an example system for generating and distributing partialRMs for offline usage in user terminals. In accordance with anembodiment of the present invention, an offline WLAN RM generator,OW-RMG, 201 takes as inputs a global RM from a global RM database 202and a list of WLAN APs to be included in a partial RM from an APselector for partial RMs 203. In order to reduce a size of a partial RM,it is desirable to include only a subset of all APs in a partial RM tobe stored on a user terminal. The AP selector for partial RMs 203 helpsachieve this goal by identifying APs which are relevant to theperformance of partial RMs. The AP selector for partial RMs 203 maycomprise a memory. The selection of APs by the AP selector for partialRMs 203 may be based at least in part on APs observed by a user terminal206. The OW-RMG 201 may further refine the list of APs received from theselector 203 based upon a set of at least one criterion. The OW-RMG 201may compress identifiers of a subset of APs in order to reduce a size ofa partial RM file. The OW-RMG 201 generates partial RMs based upon theseinputs and transfers them for storage to the offline WLAN RM database204. The partial RMs needed by the user terminal 206 are thentransferred by the offline WLAN RM database 204 to the RM offlinedownload server 205. In an embodiment of the invention, the offline WLANRM database 204 may be comprised within the OW-RMG 201. The offline WLANRM database may store partial RM belonging to different batches. Herein,a batch refers to a version of a partial radio map file. For example, abatch may comprise partial RMs created during a certain time period, forexample. In an embodiment of the invention, partial RM files aregenerated on a monthly basis such that there may be a “September batch”of partial RMs, an “October batch” of partial RMs and a “November batch”of partial RMs, for example. In another example embodiment, there may bea week 40 batch of partial RMs, comprising partial RMs generated duringweek 40 of a year, or a week 44 batch of partial RMs, comprising partialRMs generated during week 44 of a year, for example.

From the download server, a partial RM file may be downloaded by theuser terminal 206 or any other user terminal. The user terminal may havethe structure and circuitry of user terminal 102 of FIG. 1, for example.The user terminal may include at least one antenna in communication withat least one transmitter and at least one receiver to enablecommunication with the download server. Similarly, the download servermay include at least one antenna in communication with at least onetransmitter and at least one receiver to enable communication with theuser terminal. The download server may further include a processorconfigured to provide signals to and receive signals from thetransmitter and receiver, respectively.

In an embodiment of the invention, the user terminal 206 may transmit arequest for online positioning to the positioning server 207. Therequest for online positioning may contain a list of APs observed by theuser terminal at a location. The list may comprise just one AP or it maycomprise more than one APs. The location may comprise an areasurrounding a geographical position, for example. The list of APs maycomprise a list of at least one AP identity. An AP identity may comprisea service set identification, SSID, and/or a basic service setidentifier, BSSID. In some embodiments, the list comprises identities ofbase stations. The positioning server obtains a global RM from theglobal RM database 202, estimates a location of the user terminal basedupon the global RM and the list of APs, and sends the location estimateback to the user terminal. The positioning server 207 may also send thelist of APs and/or the location estimate to the partial RM qualitycontroller 208. If the positioning server sends only the list of APs butnot the location estimate to the partial RM quality controller 208, thepartial RM quality controller may itself determine a location estimatebased upon the list of APs received from the positioning server 207 anda global RM obtained from the global RM database 202. The partial RMquality controller 208 may also obtain partial RMs belonging todifferent batches from the offline WLAN RM database 204. Based uponpartial RMs belonging to different batches and the list of APs receivedfrom the positioning server, the partial RM quality controller 208 maygenerate estimates of the location based upon partial RMs of differentbatches. Comparing these location estimates to the location estimatebased upon a global RM, statistics reflecting positioning availabilityand positioning accuracy of partial RMs of a certain batch when comparedto a global RM, may be generated. These statistics may also be used tocompare a relative quality of partial RMs from different batches.Finally, these statistics may be used to determine whether a userterminal should update its partial RM or not.

Global RM database 202, AP selector for partial RMs 203, Offline WLAN RMgenerator 201, Offline WLAN RM database 204, RM offline download server205, positioning server 207 and partial RM quality controller 208 may beimplemented as standalone nodes in a network, or alternatively at leasttwo and optionally even all of them may be implemented as functions in asingle physical server.

FIG. 3 shows an apparatus embodying a process for determining a qualityof a partial RM according to an example embodiment of the invention. Asan example, apparatus 300 may be comprised in the partial RM qualitycontroller 208 of FIG. 2. Apparatus 300 comprises processors 301, 303,304, 305, 306 and, linked to these processors, a memory 307. Theprocessors 301, 303, 304, 305, 306 may, for example, be embodied asvarious means including circuitry, at least one processing core, one ormore microprocessors with accompanying digital signal processor(s), oneor more processor(s) without an accompanying digital signal processor,one or more coprocessors, one or more multi-core processors, one or morecontrollers, processing circuitry, one or more computers, various otherprocessing elements including integrated circuits such as, for example,an application specific integrated circuit, ASIC, or field programmablegate array, FPGA, or some combination thereof. A processor comprisingexactly one processing core may be referred to as a single-coreprocessor, while a processor comprising more than one processing coremay be referred to as a multi-core processor. Accordingly, althoughillustrated in FIG. 3 as single processors, in some embodiments theprocessors 303, 304, 305, 306 may comprise a plurality of processors orprocessing cores. Similarly, processors 303, 304, 305, 306 may beembodied within one processor 301. In some embodiments, at least one ofprocessors 303, 304, 305 and 306 are implemented at least in part insoftware, which software may be run on processor 301. Memory 307 storescomputer program code for supporting determining a quality of a partialRM. Processors 301, 303, 304, 305, 306 are configured to executecomputer program code stored in memory 307 in order to cause theapparatus to perform desired actions. Apparatus 300 further comprisesmemory 302. Memory 302 may be used, at least in part, to store inputdata needed for operations of the apparatus 300 or output data resultingfrom operation of the apparatus 300. Apparatus 300 could be comprised ina server or any other suitable device. Apparatus 300 could equally be amodule, like a chip, circuitry on a chip or a plug-in board, for use ina server or for any other device. Optionally, apparatus 300 couldcomprise various other components, such as for example at least one of auser interface, a further memory and a further processor. Memory 302 andmemory 307 may be distinct memories, or alternatively memory 307 may becomprised in memory 302, or memory 302 may be comprised in memory 307.

Interface 309, which may be a data interface, receives a list of APsthat a user terminal has detected at a location. The list may comprisejust one AP or it may comprise more than one APs. The location maycomprise an area surrounding a geographical position, for example. Theset of APs may comprise a list of at least one AP identity. An APidentity may comprise a service set identification, SSID, and/or a basicservice set identifier, BSSID. In some embodiments, the list comprisesidentities of base stations. The list of APs may be comprised in anonline positioning request transmitted by a user terminal to apositioning server, such as positioning server 207 of FIG. 2, forexample. The list of APs is transmitted by the interface 309 to thepartial RM location unit 305. Interface 309 may also receive furtherinformation, such as signal strengths of received radio signals, andtransmit to the partial RM location unit 305. The partial RM locationunit 305 may further receive a partial RM from a database such as theoffline WLAN RM database 204 of FIG. 2, for example. In anotherembodiment of the invention, the partial RM location unit 305 mayreceive a partial RM from a memory comprised in the apparatus 300, suchas memory 302, or it may receive the partial RM from the interface 309.Interface 309 may receive the partial RM from a memory not comprised inthe apparatus 300, such as memory comprised in the offline WLAN RMdatabase 204 of FIG. 2, for example. Based upon the list of APs and apartial RM, the partial RM location unit 305 estimates a location wherethe list of APs was detected. A result of the estimation may be a validestimate of the location or an invalid estimate of the location. Aninvalid estimate is said to result if the estimation is unsuccessful,thereby yielding no position estimate, for example. A result of theestimation may be stored in a memory location or it may be transmittedto the quality unit 304. In case no valid estimate of the location isobtained, the partial RM location unit 305 may transmit an indication tothe quality unit 304 that a valid estimate based upon a partial RM wasnot obtained. In case a valid estimate of the location is obtained, thepartial RM location unit 305 may transmit the estimate to the qualityunit 304.

The full RM location unit 303 obtains an estimate of a location wherethe list of APs was detected, based upon a full RM. The estimate basedupon a full RM may be called a reference position. A full RM is a RMfrom which the partial RM used by the partial RM location unit 305 wasderived. The full RM may contain a higher number of APs compared to thepartial RM, for example. The full RM location unit 303 may obtain theestimate based upon a full RM from the interface 309. The interface 309may receive the estimate based upon full RM from a positioning sever,such as positioning server 207 of FIG. 2, for example. In anotherembodiment of the invention, the full RM location unit 303 may obtain acopy of the full RM and may estimate a location where the list of APswas detected, based upon the full RM and the list of APs. The full RMlocation unit 303 may obtain a copy of the full RM from a memorycomprised in the apparatus 300, such as memory 302, or it may receivethe full RM via the interface 309. Interface 309 may receive the full RMfrom a memory not comprised in the apparatus 300, such as memorycomprised in the global RM database 202 of FIG. 2, for example. If aresult of the estimation is a valid estimate of the location, the fullRM location unit 303 transmits the estimate of the location to thequality unit 304. In case no valid estimate of the location is obtained,the full RM location unit 303 may transmit an indication to the qualityunit 304 that a valid estimate based upon a full RM was not obtained.

The quality unit 304 receives an estimate of a location based upon afull RM from the full RM location unit 303 and an estimate of thelocation based upon a partial RM from the partial RM location unit 305,and compares the two estimates. A result of the comparison may be thedistance between the two estimates. Another result of the comparison maybe a determination of whether the estimate based upon the full RM iscomprised within an uncertainty area of the estimate based upon thepartial RM or not. Another result of the comparison may be an indicationas to whether a valid estimate of the position was obtained or not. Incase a valid estimate of a location based upon a partial RM was notobtained, but a valid estimate of the position based upon a full RM wasobtained, a result of the comparison may be an indication to thiseffect. In case a valid estimate of a location based upon a partial RMwas obtained, but a valid estimate of the position based upon a full RMwas not obtained, a result of the comparison may be an indication tothis effect. A situation when a valid estimate of a location based upona partial RM may be obtained, but a valid estimate of the position basedupon a full RM may not be obtained may arise when an outlier AP isexcluded from the partial RM but is comprised in the full RM, forexample. An AP may be an outlier if it is located so far away from otherAPs in a list of APs that its inclusion in position determination willbe meaningless. For example, if there are five APs in the list and oneof them is location 1000 km away from the others, it may be excluded.

A quality of the partial RM relative to the full RM may be determinedbased upon a comparison of the estimates. For example, if a differencebetween an estimate based upon a partial RM and an estimate based upon afull RM is small, the partial RM may be determined to have good quality.Also, if a valid estimate of a location was obtained with a full RM butan invalid estimate was obtained using a partial RM, the partial RM maybe determined to have poor quality.

In an embodiment of the invention, the quality unit 304 may determine arelative quality of two partial RMs, based at least in part oncomparison of location estimates based upon the two partial RMs with alocation estimate based upon a full RM. For example, the partial RMlocation unit 305 may send a first and a second location estimate to thequality unit 305. The first location estimate may be based upon a firstpartial RM and the second estimate may be based upon a second partialRM. The first partial RM may be generated correspond to a geographicalarea and a second partial RM may be generated corresponding to the samegeographical area, but after an interval of time, say one week. Thequality unit 304 may compare the first location estimate to an estimatebased upon a full RM and store a first result of the comparison. Thefirst result may be a distance between the first location estimate andthe estimate based upon a full RM. The quality unit 304 may furthercompare the second location estimate to the estimate based upon the fullRM and store a second result of the comparison. The second result may bea distance between the second location estimate and the estimate basedupon a full RM. The quality estimate may compare the first result andthe second result and may determine a relative quality of the firstpartial RM and the second partial RM. For example, if the distancebetween the first location estimate and the estimate based upon a fullRM and less than the distance between the second location estimate andthe estimate based upon the full RM, the first partial RM may bedetermined to have a better quality compared to the second partial RM.

In another embodiment of the invention, the quality unit 304 determinesthat a first partial RM has better quality compared to the second RM ifa valid estimate of a location is obtained based upon the first partialRM and a valid estimate of the location was not obtained based upon thesecond partial RM.

In some embodiments of the invention, a location estimate may be anaverage of several location estimates, each corresponding to a differentlist of APs. Two lists of APs may be considered different if even one APis different between the two lists.

In an embodiment of the invention, the full RM location unit may providean estimate of the location based upon signal from a GNSS, for example.

In an embodiment of the invention, the quality unit 304 may cause apositioning client to download a partial RM, based at least on acomparison of a quality of a partial RM with a quality of a full RM orwith quality of another partial RM. The positioning client may becomprised in a user terminal.

FIG. 4 is a flow diagram showing operations for determining quality ofpartial RMs in accordance with at least one embodiment of the invention.The method may be executed by an apparatus, such as apparatus 300 ofFIG. 3, for example. In step 401, a list of APs observed by a userterminal at a location is received. The location may comprise an areasurrounding a geographical position, for example. The list of APs maycomprise just one AP or it may comprise more than one APs. The list ofAPs may comprise a list of at least one AP identity. An AP identity maycomprise a service set identification, SSID, and/or a basic service setidentifier, BSSID. The list of APs may be comprised in an onlinepositioning request transmitted by a user terminal to a positioningserver, such as positioning server 207 of FIG. 2. In step 402, it isdetermined whether an estimate of the location where the APs comprisedin the list of APs were observed, based upon a full RM, is available. Afull RM is a global RM which is likely to result in most accuratepositioning estimate and highest availability, among all RMs. Anestimate based upon a full RM may be called a reference position, forexample. If an estimate based upon a full RM is available, the processproceeds to step 405, else the process proceeds to step 403. In step403, an estimate of the location based upon the full RM is determined.In step 404, if a valid estimate of the location was obtained, theprocess moves to step 405. Else if a valid estimate was not obtained byutilizing a full RM, the process proceeds to step 409, where itterminates.

In step 405, a partial RM is selected from a batch of partial RMs suchthat the selected partial RM corresponds to the location where the APsreceived in step 401 were observed. In step 406, an estimate of thelocation is determined based upon the list of APs received in step 401and the partial RM selected in step 405. The estimate may be a validestimate of the location or the estimate may be invalid. In step 407,the location estimate determined in step 406 is compared with thelocation estimate based upon a full RM and statistics resulting from thecomparison are stored in a memory. For example, if a valid estimate ofthe location was obtained in step 405, the statistics may comprise adifference between a location estimate based upon the partial RM and thelocation estimate based upon a full RM, for example. In anotherembodiment of the invention, the statistics may comprise an indicationof whether the estimate based upon the full RM is comprised within anuncertainty area of the estimate based upon the partial RM or not. Inyet another embodiment of the invention, the statistics may comprise anindication of whether a valid estimate of location based upon a partialRM was obtained or not.

If a valid estimate was not obtained in step 405, the statistics maycomprise an indication that a valid estimate was not obtained based upona partial RM, for example. Note that other statistics can also beutilized and the invention is not restricted to statistics describedherein.

In another embodiment of the invention, the process of FIG. 4 may berepeated for a plurality of lists of APs such that statistics computedin step 407 may be averaged over the plurality of lists of APs.

In step 408, based upon the statistics determined in step 407, a qualityof a partial RM compared to a full RM may be determined. Based upon thedetermined quality of a partial RM, it may be determined where a userterminal utilizing the partial RM needs to download a newer version ofthe partial RM, such as one from a newer batch, for example.

In another embodiment of the invention, steps 405, 406 and 407 may berepeated for a plurality of batches of partial RMs such that qualitiesof partial RMs belonging to different batches may be compared. Forexample, partial RMs comprised in a first batch and a second batch maybe compared based upon a difference between location estimates basedupon partial RMs from the first and the second batch and the locationestimate based upon a full RM.

In an embodiment of the invention, a first partial RM may be determinedto have a better quality compared to a second RM if a valid estimate ofa location is obtained based upon the first partial RM and a validestimate of the location was not obtained based upon the second partialRM. In another embodiment of the invention, statistics corresponding toa first partial RM may be compared to statistics corresponding to asecond partial RM to determine a relative quality of the first partialRM and the second partial RM. The first partial RM may be generatedcorrespond to a geographical area and a second partial RM may begenerated corresponding to the same geographical area, but after aninterval of time, say one week. If a distance between an estimate of alocation based upon the first partial RM and a reference position isless than a distance between an estimate of a location based upon thesecond partial RM and the reference position, the first partial RM maybe determined to have a better quality compared to the second partialRM.

In some embodiments of the invention, a location estimate may be anaverage of several location estimates, each corresponding to a differentlist of APs. Two lists of APs may be different if even one AP isdifferent between the two lists.

In an embodiment of the invention, the full RM location unit may providean estimate of the location based upon signal from a GNSS, for example.

If desired, the different functions discussed herein may be performed ina different order and/or concurrently with each other. Furthermore, ifdesired, one or more of the above-described functions may be optional ormay be combined.

FIG. 5 demonstrates how quality of two batches of partial radio maps maybe compared, according to an embodiment of the invention. Data shown inFIG. 5 represents two batches of partial RMs, a first batch which wasgenerated during week 40 of a year and a second batch which wasgenerated during week 44 of the same year. Say, the current week is week48 the year. Resultantly, position estimate availability with thepartial RMs may be computed up to week 47. For the first batch, analysiscan be made for a 7 week period starting from week 40 and ending in week47 and for the second batch, analysis can be made for a 3 week periodstarting from week 44 and ending in week 47. Bar charts in FIG. 5 show achange in availability of partial RMs as they become outdated. Forexample, from the bar chart corresponding to the first batch or the week40 batch, it can be seen that when the batch is 5 weeks old (week 45 inthe first batch), availability of the partial RM drops by 15%. However,during the same week, a partial RM from the second batch shows a drop inavailability of less than 10%. Hence, if an acceptable level ofavailability drop is 10% in a positioning system, for example, then fromFIG. 5, it may be concluded that a new batch of partial RMs need to begenerated every 4 weeks to meet the desired level of availabilityperformance of the positioning system.

In an embodiment of the invention, a positioning client, such as theuser terminal 102, for example, may implement the methods according tothe invention.

In another embodiment of the invention, availability with a partial RMmay be compared to availability with a full RM to determine aperformance of the partial RM. For example, say availability with apartial RM is 60% and availability with a full RM is 62%. Whileavailability with the partial RM is quite low in absolute terms, itstill may be acceptable because availability with the full RM is 62%. Ifhowever, availability with the full RM is 90% and availability with apartial RM is 60%, then the partial RM likely needs to be updated.

Without in any way limiting the scope, interpretation, or application ofthe claims appearing below, a technical effect of one or more of theexample embodiments disclosed herein is to reduce a number of times apartial RM needs to be downloaded by a user terminal. Another technicaleffect of one or more of the example embodiments disclosed herein is toreplace an old partial RM with its new version only if the new versionis significantly different from the old version.

Embodiments of the present invention may be implemented in software,hardware, application logic or a combination of software, hardware andapplication logic.

The software, application logic and/or hardware may reside on memory307, the processor 301 or electronic components, for example. In anexample embodiment, the application logic, software or an instructionset is maintained on any one of various conventional computer-readablemedia. In the context of this document, a “computer-readable medium” maybe any media or means that can contain, store, communicate, propagate ortransport the instructions for use by or in connection with aninstruction execution system, apparatus, or device, such as a computer,with one example of a computer described and depicted in FIG. 3. Acomputer-readable medium may comprise a computer-readable non-transitorystorage medium that may be any media or means that can contain or storethe instructions for use by or in connection with an instructionexecution system, apparatus, or device, such as a computer. The scope ofthe invention comprises computer programs configured to cause methodsaccording to embodiments of the invention to be performed.

Although various aspects of the invention are set out in the independentclaims, other aspects of the invention comprise other combinations offeatures from the described embodiments and/or the dependent claims withthe features of the independent claims, and not solely the combinationsexplicitly set out in the claims.

It is also noted herein that while the above describes exampleembodiments of the invention, these descriptions should not be viewed ina limiting sense. Rather, there are several variations and modificationswhich may be made without departing from the scope of the presentinvention as defined in the appended claims.

We claim:
 1. An apparatus, comprising: a processor configured todetermine a first result of estimating a position based at least in parton a first partial radio map; the processor further configured toperform a first comparison of the first result to a reference position;and a memory configured to store a second result based upon the firstcomparison, the processor further configured to determine a third resultof estimating the position based at least in part on a second partialradio map; the processor further configured to perform a secondcomparison of the third result to the reference position; and theprocessor further configured to determine a quality of the first partialradio map relative to a quality of the second partial radio map based atleast in part on the first comparison and the second comparison.
 2. Theapparatus of claim 1, wherein if the first result is a valid estimate ofthe position, the second result is at least one of a difference betweenthe first result and the reference position and an indication of whetherthe reference position is comprised within an uncertainty area of thefirst result or not.
 3. The apparatus of claim 2, wherein the processoris further configured to cause transmission of a partial radio map to auser terminal based at least in part on at least one of the first resultand the second result.
 4. The apparatus of claim 1, wherein the secondresult is an indication of whether a valid estimate was obtained or not.5. The apparatus of claim 1, wherein the first comparison comprisesdetermining a first difference between the first result and thereference position; and wherein the second comparison comprisesdetermining a second difference between the third result and thereference position.
 6. The apparatus of claim 1, wherein the quality ofthe first radio map is determined to be better relative to the qualityof the second radio map if the first result is a valid estimate of theposition and the third result is not a valid estimate of the position.7. The apparatus of claim 1, wherein the quality of the first radio mapis determined to be better relative to the quality of the second radiomap if a distance between the position estimated based upon the firstpartial radio map and the reference position is less than a distancebetween the position estimated based upon the second partial radio mapand the reference position.
 8. The apparatus of claim 1, wherein theprocessor is further configured to cause transmission of a partial radiomap to a user terminal based at least in part on the quality of thefirst partial radio map relative to the quality of the second partialradio map.
 9. The apparatus of claim 1, wherein the reference positionis an estimate of the position based at least in part on at least one ofa full radio map and a navigation satellite based system.
 10. A method,comprising: determining a first result of estimating a position based atleast in part on a first partial radio map; performing a firstcomparison of the first result to a reference position; determining athird result of estimating the position based at least in part on asecond partial radio map; performing a second comparison of the thirdresult to the reference position; and determining a quality of the firstpartial radio map relative to a quality of the second partial radio mapbased at least in part on the first comparison and the secondcomparison.
 11. The method of claim 10, wherein if the first result is avalid estimate of the position, the second result is at least one of adifference between the first result and the reference position and anindication of whether the reference position is comprised within anuncertainty area of the first result or not.
 12. The method of claim 10,wherein the second result is an indication of whether a valid estimatewas obtained or not.
 13. The method of claim 10, further comprising:causing transmission of a partial radio map to a user terminal based atleast in part on the second result.
 14. The method of claim 10, whereinthe first comparison comprises determining a first difference betweenthe first result and the reference position; and wherein the secondcomparison comprises determining a second difference between the thirdresult and the reference position.
 15. The method of claim 10, whereinthe quality of the first radio map is determined to be better relativeto the quality of the second radio map if the first result is a validestimate of the position and the third result is not a valid estimate ofthe position.
 16. The method of claim 10, wherein the quality of thefirst radio map is determined to be better relative to the quality ofthe second radio map if a distance between the position estimated basedupon the first partial radio map and the reference position is less thana distance between the position estimated based upon the second partialradio map and the reference position.
 17. The method of claim 10,wherein the processor is further configured to cause transmission of apartial radio map to a user terminal based at least in part on thequality of the first partial radio map relative to the quality of thesecond partial radio map.
 18. The method of claim 10, wherein thereference position is an estimate of the position based at least in parton at least one of a full radio map and a navigation satellite basedsystem.
 19. A method, comprising: determining a first result ofestimating a position based at least in part on a first partial radiomap; determining a second result of estimating the position based atleast in part on a second partial radio map; and determining a qualityof the first partial radio map relative to a quality of the secondpartial radio map based at least in part on the first result and thesecond result, wherein the first partial radio map is generated tocorrespond to a geographical area and the second partial radio map isgenerated corresponding to the same geographical area, but after aninterval of time.
 20. The method of claim 19, further comprising: if thefirst result is a valid estimate of the position and the second resultis an invalid estimate of the position, determining that the firstpartial radio map is of a better quality compared to the second partialradio map.
 21. The method of claim 19, wherein the first partial radiomap and the second partial radio map are based upon data belonging todifferent time periods.